1. Field of the Invention
One or more exemplary embodiments of the present general inventive concept relate to a semiconductive roller used in an image-forming apparatus utilizing electrophotography, and more particularly, to a semiconductive roller capable of inhibiting surface migration phenomenon of free epichlorohydrin (ECH) component originated from a hydrin rubber, which has residues of a hydrin-based monomer so as to provide electrical conductivity.
2. Description of the Related Art
Electrophotographic image-forming apparatuses used in facsimile machines, laser printers, copying machines, and the like form a toner image as follows. First, a surface of a photosensitive layer of an electrophotographic photoreceptor is uniformly and electrostatically charged by a charging roller, and then the charged surface is exposed to a pattern of light, thus forming an electrostatic latent image. Then, a toner is provided in a vicinity of the electrostatic latent image by a developing roller, and toner droplets or particles collect in either charged or uncharged regions to form a toner image on the surface of the photosensitive layer. A resulting toner image formed on the photosensitive layer of the electrophotographic photoreceptor may be transferred to a suitable final or intermediate image receiving member such as a plain paper by a transfer member such as a transfer roller or a transfer belt, or the photosensitive layer may function as a final receptor to receive the toner image. Then, the toner image transferred onto the surface of the final or intermediate image receiving member is fixed.
A semiconductive roller can be used as the charging roller, the developing roller, and the transfer roller. U.S. Publication No. 2012/0202663 discloses a semiconductive roller prepared by applying a cross-linked product of a mixture of a hydrin rubber, as an electroconductive component, and a rubber having an unsaturated bond, to an elastic layer of the semiconductive roller. A semiconductive roller having an elastic layer that includes carbon black as an electroconductive component is also known in the art.
However, when the carbon black is used, a non-uniform image may be formed due to non-uniform electrical conductivity if the carbon black is not uniformly dispersed. When a hydrin rubber is used, the problem of non-uniform dispersion may be decreased because the hydrin rubber has high flowability and is compatible with other rubber components constituting a matrix of the elastic layer.
However, using hydrin rubber for a semiconductive roller may cause surface migration that could deteriorate image quality of an electrophotographic image-forming apparatus. Specifically, low-molecular weight materials, which is contained in a composition to form an elastic layer of the semiconductive roller, and free epichlorohydrin (ECH) component, which is contained in the hydrin rubber and is not bonded to the other rubber components due to incomplete cross-linking, may migrate onto the surface of the elastic layer, i.e., the surface of the semiconductive roller, due to pressurization or deformation under operating conditions of an image-forming apparatus, thereby eventually contaminating the surface of the transfer roller. Such surface migration phenomenon may increase over time.
The ECH component includes an ECH monomer and a hydrin rubber oligomer having flowability. Particularly, the ECH component, which tends to have a high chemical attack property, may cause damage to a photosensitive layer formed of a material vulnerable to chemicals on the surface of a photoreceptor, thereby causing defects of images or a decreased stability of images with increasing temperature. Particularly, when a polycarbonate is contained in the surface layer of the photoreceptor, the free ECH component that has migrated to the surface may attack the polycarbonate to make the surface layer of the photosensitive layer non-uniform, thereby causing defects of images.
In a transfer roller having a foamed elastic layer, surface migration phenomenon over time may be more serious than a transfer roller having a solid elastic layer, since the former of which has a shorter surface migration pathway for the free ECH component and is more deformed during operation of an image-forming apparatus.